Image Credit: Felixir

Every 1st September, new first years arrive at Hogwarts via boat, traveling from the outskirts of Hogsmeade, across the lake, and into the boathouse. This structure stands, logically enough, at the edge of the lake, and can be reached via a pathway from the courtyard, consisting of a long and winding stairway down the cliff face. A hidden passageway accessible from the inside of the boathouse leads up through the cliff itself, and emerges onto a patch of lawn which lies in the shadow of the castle.

All of the Hogwarts boats are stored here when not in use. You are free to take them out onto the lake, as long as you have permission from the groundskeeper to do so. Everything you might need for a trip out in the boats is hanging up around the walls, including oars and life jackets. Be sure to put everything back where you found it once you're done with it. Including - and especially - the boats themselves.